On Tue, 17 Mar 2020 at 14:22, Qian Cai <cai@xxxxxx> wrote: > > Even if KCSAN is disabled for kmemleak, update_checksum() could still > call crc32() (which is outside of kmemleak.c) to dereference > object->pointer. Thus, the value of object->pointer could be accessed > concurrently as noticed by KCSAN, > > BUG: KCSAN: data-race in crc32_le_base / do_raw_spin_lock > > write to 0xffffb0ea683a7d50 of 4 bytes by task 23575 on cpu 12: > do_raw_spin_lock+0x114/0x200 > debug_spin_lock_after at kernel/locking/spinlock_debug.c:91 > (inlined by) do_raw_spin_lock at kernel/locking/spinlock_debug.c:115 > _raw_spin_lock+0x40/0x50 > __handle_mm_fault+0xa9e/0xd00 > handle_mm_fault+0xfc/0x2f0 > do_page_fault+0x263/0x6f9 > page_fault+0x34/0x40 > > read to 0xffffb0ea683a7d50 of 4 bytes by task 839 on cpu 60: > crc32_le_base+0x67/0x350 > crc32_le_base+0x67/0x350: > crc32_body at lib/crc32.c:106 > (inlined by) crc32_le_generic at lib/crc32.c:179 > (inlined by) crc32_le at lib/crc32.c:197 > kmemleak_scan+0x528/0xd90 > update_checksum at mm/kmemleak.c:1172 > (inlined by) kmemleak_scan at mm/kmemleak.c:1497 > kmemleak_scan_thread+0xcc/0xfa > kthread+0x1e0/0x200 > ret_from_fork+0x27/0x50 > > If a shattered value was returned due to a data race, it will be > corrected in the next scan. Thus, annotate it as an intentional data > race using the data_race() macro. > > Signed-off-by: Qian Cai <cai@xxxxxx> > --- > mm/kmemleak.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/kmemleak.c b/mm/kmemleak.c > index e362dc3d2028..d3327756c3a4 100644 > --- a/mm/kmemleak.c > +++ b/mm/kmemleak.c > @@ -1169,7 +1169,12 @@ static bool update_checksum(struct kmemleak_object *object) > u32 old_csum = object->checksum; > > kasan_disable_current(); Suggested: + kcsan_disable_current(); > - object->checksum = crc32(0, (void *)object->pointer, object->size); > + /* > + * crc32() will dereference object->pointer. If an unstable value was > + * returned due to a data race, it will be corrected in the next scan. > + */ > + object->checksum = data_race(crc32(0, (void *)object->pointer, > + object->size)); This will work with the default config, because for word-sized-aligned writes no marking is enforced. But this will still cause a data race if the write is e.g. due to a memcpy. There are already markers for KASAN around, so the most reliable thing is to just disable KCSAN in this region. > kasan_enable_current(); Suggested: + kcsan_enable_current(); Thanks, -- Marco > return object->checksum != old_csum; > -- > 2.21.0 (Apple Git-122.2) >
